1.2 Comparing Exchange 2000 and Exchange 5.5

Chapter 1 - Introduction
Monitoring and Managing Microsoft Exchange 2000 Server
by Mike Daugherty
Digital Press 2001

The Microsoft Exchange Server 5.5 architecture includes the components shown in Figure 1.1:

Figure 1.1: Exchange 5.5 architecture

• MAPI Clients . The most commonly deployed client is the Outlook client. It communicates with the Exchange Information Store and Exchange Directory Services using MAPI and RPC.

• Directory . The Exchange 5.5 Directory Service stores system-wide information about all e-mail users and Exchange objects, and ensures that this information is replicated to other Exchange servers throughout the organization.

• Information Store . The Information Store is responsible for maintaining each user s private information store and the public information store.

• MTA . The Exchange 5.5 Message Transport Agent (MTA) is based on the X.400 standard and is responsible for transferring messaging information from one server to another.

• Connectors . Connectors are available to facilitate the exchange of messages between two Exchange Routing Groups, and between the Exchange environment and foreign environments such as Microsoft Mail, cc:Mail, and Lotus Notes.

• System Attendant . The System Attendant monitors the other components.

• Admin . The Exchange Admin program is the administrators primary tool for managing the Exchange environment. Most additions and changes to user mailboxes and messaging system components are made using this program.

The Exchange 2000 architectural diagram as shown in Figure 1.2 is more complicated. Even those components that are retained from earlier versions of Exchange have been significantly changed.

Figure 1.2: Exchange 2000 architecture

The Exchange 2000 architecture relies on Internet Information Server (IIS) to provide access to/from Internet protocols. The Exchange 2000 Information Store has new capabilities. The Windows 2000 Active Directory now supplies the directory services.

IIS acts as the protocol server for Exchange 2000, managing the socket connections to the client. Internet protocols such as SMTP, IMAP, and POP are hosted within the IIS environment rather than being part of Exchange. Each service is implemented as a virtual server and each IIS instance can host multiple copies of the same protocol or multiple different protocols.

Exchange 2000 can use the IIS Front End/Back End (FE/BE) architecture to improve horizontal scalability. The Front End system serves as a protocol parser and the Back End system is the interface to the store. An IMAP or POP client connects to the FE system and specifies the users mailbox. Once the user is authenticated, the FE system consults the Windows 2000 Active Directory to determine which BE system has the users data. Roundrobin DNS can be used to make the entire group of IIS Front End systems appear to the client as a single system with a single IP address. This can be used to balance the user load across all of the FE systems. When the user load exceeds the capabilities of the FE systems, additional FE systems can be added without changing the client configuration.

Note 

MAPI clients, such as Outlook, do not use Internet protocols. Therefore, the IIS Front End/Back End architecture has no advantages if you only have MAPI clients.

Messages submitted by an Internet client (e.g., HTTP, SMTP, NNTP, POP or IMAP) are stored in their native MIME format. Storing the messages in their native format means that the messages do not need to be converted when the client retrieves the message. Of course, if a MAPI client such as Outlook accesses the same MIME message, the message will be converted to Exchange Rich Text Format.

Epoxy is a high-performance inter-process communication facility that uses shared memory to communicate between IIS processes and Information Store processes running on the same system.

The Exchange Installable File System (IFS) is a file system interface to the Exchange Information Store. One of its purposes is to reduce memory copies and disk I/O for inbound and outbound messages. This allows the protocol servers to retain the appearance of a one-to-one correspondence between messages and files, even though the actual contents are stored in a single NTFS file.

Exchange 2000 no longer contains a directory or a directory service. Instead, it relies upon the Active Directory component in Windows 2000. If you are familiar with the Exchange 5.5 directory service, with X.500, with LDAP directories, or with Netware NDS, then you will find the Windows 2000 Active Directory similarbut more complex. Exchange 2000 uses the Windows 2000 Active Directory to authenticate users, to locate other directory servers, and to supply infrastructure and configuration information.

Exchange 2000 also depends on the Active Directory Global Catalog to replicate Exchange configuration data to all servers within a forest. The Windows 2000 Global Catalog contains all objects from the local Windows 2000 domain, plus selected attributes for objects from other domains in the Windows 2000 forest.

Exchange 2000 extends the Windows 2000 Active Directory schema to add new, Exchange- related properties to the user objects. These properties include the information store that holds the users mailbox, user-specific quotas, and delivery restrictions. Configuration data is placed in a special Exchange container. Since Exchange is no longer responsible for the directory service, it is also no longer responsible for replicating the directory information throughout the environment. Replication of all Active Directory objectsincluding the Exchange objects and propertiesis performed by Windows 2000. Tailoring the replication process is also done using Windows 2000.

All Windows 2000 Active Directory objects and propertiesincluding those added by Exchange 2000are managed using the Windows 2000 Microsoft Management Console (MMC). Exchange users are just Windows 2000 users with the rights to use Exchange. The Exchange properties associated with a user are just another property sheet for the Windows 2000 user and is managed using the same Active Directory Users and Computers MMC snap-in that is used to manage other user-related properties.

The Exchange 2000 message transfer service uses the Windows 2000 SMTP Routing Engine. The old Exchange 5.5style MTA is still available in Exchange 2000. However, by default, it is not configured. It is only used if needed to handle X.400 or for transport in environments that contain both Exchange 5.5 and Exchange 2000 servers.

The Information Store has also changed. Each Exchange 5.5 server had a single large private information store containing the mailboxes for all users. The size of the private information store grew in direct relationship with the number of users and the numbers of messages retained by these users. The resulting private information storestored as a single Windows NT file could easily reach many gigabytes in size spanning multiple physical disks. The most significant problem caused by the large size is the increased amount of time required to restore the file from backup tapes should the file be corrupted. See Figure 1.3.

Figure 1.3: Exchange Information Store architecture

The Exchange 2000 Information Store has been significantly enhanced to improve scalability and availability. These changes will affect Exchange organizational designs and will also affect how Exchange is managed once it is deployed. The Exchange 2000 Information Store (also often referred to as the WebStore) can be partitioned into up to four Storage Groups. Each Storage Group is managed by a separate Extensible Storage Engine (ESE) instance and can contain up to five databases. All databases within a Storage Group share the same set of transaction log files. Each database actually includes two files:

• An EDB file similar to those found in Exchange 5.5

• An STM file that stores messages submitted by Internet clients (e.g., HTTP, SMTP, NNTP, POP or IMAP) in their native format

The changes to the information store influence both the placement of user mailboxes and the backup/recovery strategy for Exchange 2000. An updated backup utility that understands and takes advantage of the new Information Store architecture is included with Exchange 2000.

Even much of the basic terminology has changed.

In Exchange 5.5, a site was both a routing topology and management boundary. Most good Exchange 5.5 designs began by defining sites based on network topology and then adjusted the design to address corporate administrative needs. Trying to meet both topology and management requirements with a single structure usually required compromises that resulted in a less-than -desired administrative structure. One of the key advantages of Exchange 2000 is the separation of these two concepts. The Exchange 5.5 site concept has been replaced by two separate structures in Exchange 2000. An Exchange 2000 routing group defines the routing topology boundary and an Exchange 2000 administrative group defines the management boundary.

Since the Exchange 5.5 site has disappeared, the Exchange 5.5 Site Connector has also been replaced. The corresponding Exchange 2000 concept is the Routing Group Connector.

The Exchange 5.5 IMS has been replaced by the Exchange 2000 SMTP Virtual Server. All of the Internet protocols can be implemented as multiple virtual servers.

Exchange 5.5 Address Book Views have been replaced by Exchange 2000 Address Lists. The familiar Global Address List (GAL) is just one of these address lists.

Most of the changes for Exchange 2000 are designed to improve scalability, performance, or reliability. However, many of the changes either directly or indirectly influence how the Exchange environment is managed.

Do not look for the familiar Exchange 5.5 Admin program. It is gone. Exchange administration is now performed by a set of MMC snap-ins. User information is maintained using the Active Directory Users and Computers snap-in. Exchange-specific components are managed using the Exchange System Manager snap-in.